1. Field of the Invention
The present invention relates to a production method of a dental ceramics material capable of expressing a color tone similar to that of dentin of a tooth easily at a low cost.
2. Description of the Conventional Art
Transparency of a human tooth is gradually decreased from enamel which is a surface layer to dentin inside the enamel in general. When a dental technician produces a dental prosthesis, a material having transparency is used on the surface side and a material having low transparency and chroma is used at the inside in order to make a color tone similar to a natural tooth.
In recent years, when a dental prosthesis is produced by a ceramics material, stabilized zirconium oxide is often used for a ceramics frame to be an inner cap such as a crown, a bridge or the like, and for a ceramics abutment which is a material for penetrating a gingival part of a dental implant, since stabilized zirconium oxide has high strength. However, since zirconium oxide is white and opaque, the ceramics frame and the ceramics abutment are visible when the material having high transparency is built on the surfaces of the ceramics frame and the ceramics abutment. So, it is not preferable aesthetically. In order to avoid this problem, a large amount of opaquers must be used before the material is built on the surface, and excessive skill is required.
Further, when the dental prosthesis is produced by a ceramics, the material having transparency is built on the surface of the ceramics frame and the ceramics abutment and baked at 1,350 to 1,600 degrees C. Thus, there is a problem that a coloring agent which has been conventionally used in a dental field is decomposed so as not to express an intended color tone.
On the other hand, a colored sintered zirconium oxide has been proposed (for example, refer to Japanese translation of PCT international application No. 2004-527280, Section Nos. 0037 and 0040). In order to produce the sintered zirconium oxide, a coloring oxidizer having an element of a group including Pr, Er, Fe, Co, Ni, Ti, V, Cr, Cu and Mn is preferably contained as a coloring agent, and Fe2O3, Er2O3, and MnO2 are preferable used. However, since this coloring agents must be added in a form of an oxide obtained by dissolving in HCl, the color may be damaged when the coloring agents are baked at 1,350 to 1,600 degrees C. Further, when the above-described various coloring agents are combined to be used, there are many agents which hardly obtain a color tone of dentin of a tooth which is required in a dental filed. Further, since the coloring agents must be added as a form of an oxide obtained by dissolving in HCl, a raw material having remarkably high cost must be used. So, there is a problem of production cost.
Further, a method for blending Er2O3, Pr6O11, Fe2O3 and ZnO to zirconium oxide containing a stabilizer so as to color dentin has been proposed (for example, refer to Japanese Patent No. 2571646). However, there is a problem that Er2O3 and the like cannot be well mixed without blending as a solution which is once dissolved by hydrochloric acid or nitric acid. Thus, Er2O3 and the like are necessarily mixed by the steps of pre-baking a powder obtained from the solution, and sintering with adding and mixing an iron compound and a zinc compound. So, the use of Er2O3 and the like is troublesome and complicated. Further, when Er2O3, Pr6O11 are used, these are decomposed at about 1,300 degrees C. Thus, there is a problem that Er2O3, Pr6O11 cannot be used at 1,350 to 1,600 degrees C. which is a baking temperature of zirconium oxide containing a general stabilizer.